Information processing system, information processing unit, control method, program and a recording medium

ABSTRACT

An information processing system includes a plurality of information processing units wirelessly communicating with each other, each of which includes a distribution data receiving section for receiving distribution data to be distributed to each of the information processing units from an information processing unit that has received the distribution data among the plurality of information processing units, a destination selection section for selecting an information processing unit that has not received the distribution data as a destination information processing unit for the distribution data from among the plurality of information processing units, and a distribution data sending section for sending the distribution data to the information processing unit selected by the destination selection section using a frequency band that is not used by another information processing unit while the other information processing unit is sending the distribution data to still another information processing unit.

TECHNICAL FIELD

The present invention relates to an information processing system,information processing unit, control method, program and recordingmedium. In particular, the present invention relates to an informationprocessing system, information processing unit, control method, programand recording medium for configuring a wireless communication network.

BACKGROUND

Recently, as higher performance and more price reduction of computersare increasingly realized, “IT” is rapidly progressed in various fields.For example, in the field of education, it is increasingly common thateach student is provided with his/her own personal computer for useduring lectures and practices. In order to give such lecturesappropriately, it is necessary to appropriately set up software for alot of personal computers for each lecture.

As functions of software are increasingly complicated, significant timeand labor are often required to set up software for a number ofcomputers. Accordingly, it is conceivable to distribute a disk image forreplacing the contents of a hard disk drive to each computer via anetwork when the same software is installed according to the samesettings. However, the data size of the disk image is generally verylarge.

FIG. 14 is a conceptual diagram showing that a disk image is distributedvia a wired network. A server device 80 communicates with a layer 2switching hub via the Gigabit Ethernet®, for example. The layer 2switching hub communicates with each of personal computers 85-1 to 85-30via the 100 Base-T Ethernet®. In this case, if the data size of the diskimage is assumed to be 5 Gbytes, distribution of the disk image iscompleted in about one hour. Thus, with the progress of recentcommunication technology, the communication speed of wired connectionhas been increased, and in most cases, there is caused no problem in thecommunication speed in distributing a disk image.

FIG. 15 is a conceptual diagram showing that a disk image is distributedvia a wireless network. A server device 90 connects to a wireless LANaccess point which is in compliance with the IEEE802.11g standard. Thewireless LAN access point communicates with each of personal computers95-1 to 95-30 at a link rate up to 54 Mbps. However, the effectivetransfer rate is about 20 Mbps. In this case, since the transfer band of20 Mbps is shared by the thirty computers, the transfer rate of onecomputer is about 0.7 Mbps. As a result, if the data size of the diskimage is assumed to be 5 Gbytes, more than sixteen hours are requiredfor distribution of the disk image.

There have been proposed various techniques relative to the ad hoc modefor wireless LAN. For example, there has been proposed a techniquewherein, when one cluster is constituted by multiple communicationdevices mutually communicating with each other in the ad hoc mode forwireless LAN, a cluster head for managing the cluster is appropriatelyselected from among these information processing units (see JapanesePublished Patent Application 2002-44003). There has also been proposed atechnique wherein, in star connection where one parent machine andmultiple child machines are connected in the ad hoc mode for wirelessLAN, a communication device to be the parent machine is selected basedon the remaining amount of a battery for driving each communicationdevice (see Japanese Published Patent Application 2003-32263).

According to the example in FIG. 14, it is possible to distribute a diskimage at a high speed. However, it is necessary to perform wiring andinstall equipment in order to configure a wired network, which is oftentroublesome. According to the example in FIG. 15, it takes too much timeto distribute a disk image. Therefore, even if distribution is startedat a closing time, the distribution is not completed by a starting timeof the next day. This causes the rate of facility operation to be verylow. Further, since the techniques disclosed in the above patentapplications aim at keeping the status of wireless communication in thead hoc mode optimum, no method for distributing data, such as a diskimage, at a high speed is mentioned.

SUMMARY OF THE PREFERRED EMBODIMENTS

The foregoing and other problems are overcome, and other advantages arerealized, in accordance with the presently preferred embodiments ofthese teachings.

In order to solve the above problem, in a first aspect of the presentinvention, there is provided an information processing system comprisinga plurality of information processing units wirelessly communicatingwith each other, in which each of the plurality of informationprocessing units comprises a distribution data receiving section forreceiving distribution data to be distributed by each of the pluralityof information processing units from an information processing unit thathas received the distribution data among the plurality of informationprocessing units, a destination selection section for selecting aninformation processing unit that has not received the distribution dataas a destination information processing unit for the distribution datafrom among the plurality of information processing units, and adistribution data sending section for sending the distribution data tothe information processing unit selected by the destination selectionsection using a frequency band that is not used by another one of theplurality of information processing units while the other one of theplurality of information processing units is sending the distributiondata to still another one of the plurality of information processingunits. Further, an information processing unit configuring theinformation processing system, a control method for the informationprocessing unit, a program for controlling the information processingunit, and a recording medium recording the program are also provided.

According to the present invention, data can be distributed to aplurality of information processing units at high speed.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of these teachings are made more evidentin the following Detailed Description of the Preferred Embodiments, whenread in conjunction with the attached Drawing Figures, wherein:

FIG. 1 shows a configuration of an information processing system.

FIG. 2 shows transmission routes along which distribution data is sentin the information processing system.

FIG. 3 shows a configuration of an information processing unit includedin the information processing system.

FIG. 4 shows a configuration of a CPU included in the informationprocessing unit.

FIG. 5 shows a process flow of the information processing unit.

FIG. 6 shows a process flow of the information processing unit sendingdistribution data;

FIG. 7 shows a process flow of the information processing unit receivingdistribution data;

FIG. 8 shows a process of sending the distribution data via wirelesscommunication in thirty minutes from the beginning.

FIG. 9 shows a process of sending the distribution data via wirelesscommunication in one hour from the beginning.

FIG. 10 shows a process of sending the distribution data via wirelesscommunication in one hour and thirty minutes from the beginning.

FIG. 11 shows a process of sending the distribution data via wirelesscommunication in two hours from the beginning.

FIG. 12 shows a process of sending the distribution data via wirelesscommunication in two hours and thirty minutes from the beginning.

FIG. 13 shows a process of sending the distribution data via wirelesscommunication in three hours from the beginning.

FIG. 14 is a conceptual diagram showing that a disk image is distributedvia a wired network.

FIG. 15 is a conceptual diagram showing that a disk image is distributedvia a wireless network.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a configuration of an information processing system 10.FIG. 2 shows transmission routes along which distribution data is sentin the information processing system 10. The information processingsystem 10 is provided indoors, for example, in a lecture room andcomprises an information processing unit 20 and information processingunits 30-1 to 30-30 which wirelessly communicate with each other. Theinformation processing unit 20 is provided, for example, on a lectureadministrator's desk. The information processing unit 20 is apredetermined information processing unit serving as a source ofdistribution for distribution data to be distributed to the informationprocessing units 30-1 to 30-30, and stores the distribution data inadvance. For example, the information processing unit 20 may read thedistribution data from a CD-ROM or the like and store it, in response toa user operation. The information processing unit 20 establishesone-to-one connection sequentially with each of the informationprocessing units 30-1 and 30-22 in the wireless LAN ad hoc mode.Thereby, the information processing unit 20 sends the distribution datasequentially to each of the information processing units 30-1 and 30-22.

The information processing units 30-1 to 30-30 are provided, forexample, on the respective student's desks. When receiving thedistribution data, the information processing unit 30-1 sends thedistribution data sequentially to each of the information processingunits 30-2 and 30-3 using a frequency band which is not used by theinformation processing unit 20 for transmission while the informationprocessing unit 20 is sending the distribution data to the informationprocessing unit 30-22. Similarly, each of the information processingunits 30-2 to 30-6, 30-11, 30-16, 30-18, 30-21 to 30-24 and 30-26 sendsthe distribution data using a frequency band which is not used by anyother information processing unit while the other information processingunit is sending the distribution data to still another informationprocessing unit.

The information processing unit may be a desktop type personal computeror a notebook type computer powered by a battery or by AC power. Thewireless communication may be performed via a wireless LAN conforming tothe IEEE802.11a/b/g standard, for example. The frequency band isdetermined by one of communication channels which can be selectively setin the wireless LAN standard. For example, in the case of theIEEE802.11a/g standard, one of twenty-seven channels can be set for eachinformation processing unit, and a different frequency band can be usedfor each channel to be set.

The distribution data is, for example, a disk image for replacing thecontents of the hard disk drive of each information processing unit.Specifically, the distribution data includes an operating system,application program(s), or setting information of parameters for theseprograms.

Thus, the information processing system 10 according to this embodimentsends distribution data concurrently using a plurality of frequencybands by combining a plurality of information processing units each ofwhich can use only one frequency band. Thus, the distribution data canbe distributed quickly by transferring it along, for example,communication routes in a tree structure to enhance the degree ofconcurrency in sending the distribution data, and using as manyfrequency bands as possible at the same time.

FIG. 3 shows a configuration of the information processing unit 30-1.The information processing unit 30-1 is an example of a firstinformation processing unit according to the present invention andcomprises a CPU-related part having a CPU 1000, a RAM 1020 and a graphiccontroller 1075 which are mutually connected via a host controller 1082,an input/output part having a communication interface 1030, a hard diskdrive 1040 and a CD-ROM drive 1060 which are connected to the hostcontroller 1082 via an input/output controller 1084, and a legacyinput/output part having a BIOS 1010, a flexible disk drive 1050 and aninput/output chip 1070 which are connected to the input/outputcontroller 1084.

The host controller 1082 connects the RAM 1020 to the CPU 1000 and thegraphic controller 1075 both of which access the RAM 1020 at a hightransfer rate. The CPU 1000 controls each part based on programs storedin the BIOS 1010 and the RAM 1020. The graphic controller 1075 acquiresimage data generated by the CPU 1000 or other device on a frame bufferprovided in the RAM 1020, and displays it on a display device 1080.Alternatively, the graphic controller 1075 may include therein the framebuffer for storing image data generated by the CPU 1000 or other device.

The input/output controller 1084 connects the host controller 1082 tothe communication interface 1030, the hard disk drive 1040 and theCD-ROM drive 1060 which are relatively high-speed input/output devices.The communication interface 1030 communicates with an external devicevia a wireless or wired network. Specifically, the communicationinterface 1030 may select one of frequency bands to communicate withanother information processing unit.

The communication interface 1030 uses an ad hoc mode for performingone-to-one communication with another information processing unit, andan infrastructure mode for communicating with a wireless LAN accesspoint. The hard disk drive 1040 stores programs and data to be used bythe information processing unit 30-1. The CD-ROM drive 1060 reads aprogram or data from a CD-ROM 1095 and stores it in the RAM 1020 via theinput/output controller 1084.

The BIOS 1010, a power control section 1065 and relatively low-speedinput/output devices such as the input/output chip 1070 are connected tothe input/output controller 1084. The BIOS 1010 stores a boot program tobe executed by the CPU 1000 at the startup time of the informationprocessing unit 30-1, and programs dependent on the hardware of theinformation processing unit 30-1. The flexible disk drive 1050 isconnected to the input/output chip 1070. The flexible disk drive 1050reads a program or data from a flexible disk 1090 and stores it in theRAM 1020 via the input/output chip 1070 and the input/output controller1084.

The power control section 1065 has a battery 1068 for driving theinformation processing unit 30-1. Also, the power control section 1065is connected to an external AC power. The power control section 1065supplies power to each part of the information processing unit 30-1 fromthe battery 1068 or the AC power. Furthermore, the power control section1065 manages strength of the battery 1068 and outputs informationindicating the battery strength to the CPU 1000. The power controlsection 1065 may power down the information processing unit 30-1 basedon an instruction from the CPU 1000, or may shift the informationprocessing unit 30-1 to a suspend state in which the power istemporarily shut down. The input/output chip 1070 connects the flexibledisk 1090, and other input/output devices via parallel, serial, keyboardand/or mouse ports.

A program to be provided for the information processing unit 30-1 isstored in a recording medium such as the flexible disk 1090, the CD-ROM1095 or an IC card, and provided by a user. The program is read from therecording medium via the input/output chip 1070 and/or the input/outputcontroller 1084, installed in the information processing unit 30-1, andexecuted.

The program shown above may be stored in an external recording medium.The recording medium may be an optical recording medium such as a DVD ora PD, a magneto-optic recording medium such as an MD, a tape medium, ora semiconductor memory such as an IC card in addition to the flexibledisk 1090 or the CD-ROM 1095. It is also possible to use a storagedevice, such as a hard disk drive or a RAM, which is provided for aserver system connected to a dedicated communication network or theInternet as the recording medium, and provide the program to theinformation processing unit 30-1 via the network. Each of theinformation processing units 30-2 to 30-30 and the informationprocessing unit 20 have almost the same configuration as the informationprocessing unit 30-1, and therefore description thereof will be omittedhere.

FIG. 4 shows a configuration of the CPU 1000. The program installed inthe information processing unit 30-1 causes the CPU 1000 to function asa distribution data receiving section 400, an unused band detectionsection 410, a destination selection section 420, a waiting time settingsection 425, a distribution data sending section 430, a suspendingsection 440, a power down section 450, a transfer route acquisitionsection 460 and a used band indicating information acquisition section470. The distribution data receiving section 400 receives distributiondata from an information processing unit that has received thedistribution data among a plurality of information processing units, andstores it in the hard disk drive 1040. For example, the distributiondata receiving section 400 may receive the distribution data from theinformation processing unit 20 which serves as a predetermined source ofdistribution, or receive the distribution data from another informationprocessing unit which has received the distribution data from theinformation processing unit 20.

The unused band detection section 410 detects a frequency band which isnot used by any other information processing unit within the range inwhich a radio wave of wireless communication by the informationprocessing unit 30-1 interferes. For example, the unused band detectionsection 410 may periodically determine, for each frequency band, whetheror not it is an unused band by giving an instruction to thecommunication interface 1030. More specifically, the unused banddetection section 410 detects a wireless LAN communication channel whichis not used by any other information processing unit for communicationby switching wireless LAN communication channels to perform frequencyhopping.

The destination selection section 420 selects from a plurality ofinformation processing units an information processing unit which hasnot received the distribution data as an information processing unit towhich the distribution data is to be sent. For example, the destinationselection section 420 may instructs the communication interface 1030 toinquire of each of the other information processing units whether thedistribution data has not been received, through an unused band. In thiscase, the destination selection section 420 selects an informationprocessing unit from among information processing units which have madea response to the inquiry to the effect that the distribution data hasnot been received. Alteratively, the destination selection section 420may select a destination information processing unit based on transferroute information acquired by the transfer route acquisition section460. As a result, the destination selection section 420 selects, forexample, the information processing unit 30-2, an example of a secondinformation processing unit which has not received the distributiondata, as a destination information processing unit to which thedistribution data is to be sent.

Preferably, if the distribution data sending section 430 finishestransmission of the distribution data, the destination selection section420 selects a destination information processing unit to which thedistribution data sending section 430 sends the distribution data next,after passage of a waiting time set by the waiting time setting section425. In this case, the waiting time setting section 425 may set thewaiting time based on the time required for transmission of thedistribution data acquired from the distribution data sending section430. For example, a longer waiting time may be set if it takes much timeto send the distribution data due to a bad radio wave condition. Thus,it is possible to assign a frequency band preferentially to aninformation processing unit having a good radio wave condition and,therefore, distribute the distribution data more efficiently.

The distribution data sending section 430 sends the distribution data tothe information processing unit 30-2 selected by the destinationselection section 420, using the unused band detected by the unused banddetection section 410. Thus, the distribution data sending section 430can send the distribution data concurrently with another informationprocessing unit sending the distribution data to still anotherinformation processing unit, using a frequency band which is not used bythat other information processing unit.

If the unused band detection section 410 cannot detect an unused band,the suspending section 440 instructs the power control section 1065 totemporarily power down the information processing unit 30-1 and shiftthe information processing unit 30-1 to a suspend state. Morespecifically, the suspending section 440 may call an API (ApplicationProgramming Interface) of the operating system or the BIOS to shift theinformation processing unit 30-1 to the suspend state. Furthermore, ifan information processing unit which has not received the distributiondata is not detected, the suspending section 440 may instruct the powercontrol section 1065 to temporarily power down the informationprocessing unit 30-1 and shift it to the suspend state.

If the distribution data has already been received, the power downsection 450 acquires information about the strength or remaining chargeof the battery 1068 from the power control section 1065 each time thedistribution data is sent to another information processing unit. If thestrength of the battery 1068 is below a level required for sending thedistribution data, the power down section 450 powers down theinformation processing unit 30-1 without sending the distribution datato the next information processing unit.

The transfer route acquisition section 460 may acquire from theinformation processing unit 20 a transfer route along which thedistribution data is to be transferred sequentially by a plurality ofinformation processing units, in association with the distribution data.In this case, the destination selection section 420 selects adestination information processing unit based on the transfer route. Forexample, the transfer route acquisition section 460 may acquire atransfer route with the number of HOPs, which indicates the number oftimes the distribution data is transferred sequentially through aplurality of information processing units, being less than apredetermined upper-limit number and with the number of destinationinformation processing units, to which the distribution data is sent bythis information processing unit, being less than predeterminedupper-limit number. Thereby, it is possible to determine an approximateupper limit of time required for sending the distribution data.

The used band indicating information acquisition section 470 may acquireused band indicating information specifying a frequency band used byeach information processing unit for wireless communication, inassociation with the distribution data, for example. In this case, theunused band detection section 410 detects an unused band based on theused band indicating information. Accordingly, if frequency bands whichdo not interfere with each other are determined beforehand, it ispossible to save time required for detecting an unused band. Thus, anunused band and a transfer route may be predetermined by the user.

A CPU in each of the information processing units 30-2 to 30-30 hasalmost the same configuration as that of the CPU 1000 shown in FIG. 4except that the sender and the destination of the distribution data aredifferent. For example, in the information processing unit 30-22, whichis an example of a third information processing unit according to thepresent invention, the destination selection section 420 selects theinformation processing unit 30-21, which is an example of a fourthinformation processing unit according to the present invention, as adestination information processing unit. The distribution data sendingsection 430 sends the distribution data to the information processingunit 30-21 concurrently with the information processing unit 30-1sending the distribution data to the information processing unit 30-2,using a frequency band which is not used by the information processingunit 30-1. The other parts of the configuration are almost the same asthose of the CPU 1000 in FIG. 4, and therefore description thereof willbe omitted.

FIG. 5 shows a process flow of the information processing unit 30-1. Ifthe information processing unit 30-1 has already received distributiondata (S500: YES), it sends the distribution data to another informationprocessing unit (S510). On the other hand, if the information processingunit 30-1 has not received the distribution data, it receives thedistribution data from another information processing unit (S520).

FIG. 6 shows a process flow of the information processing unit 30-1sending distribution data. First, the unused band detection section 410detects an unused band (S600). If an unused band cannot be detected(S610: NO), the suspending section 440 shifts the information processingunit 30-1 to a suspend state in which the information processing unit30-1 is temporarily powered down (S620). Thereby, it is possible toreduce power consumption by the information processing unit 30-1 andsuppress battery consumption. If the information processing unit 30-1 isdriven by an AC power, the suspending section 440 may return the processto step S600 without shifting the information processing unit 30-1 tothe suspend state. In this case, it is possible to check whether or notthere is any unused band more frequently and, therefore, distribute thedistribution data more quickly.

If an unused band is detected (S610: YES), then the destinationselection section 420 inquires of each of the other informationprocessing units whether the distribution data has not been received,using the unused band (S630). If the destination selection section 420does not receive a response which indicates that the distribution datahas not been received, from any of the information processing units(S635: NO), then the suspending section 440 shifts the informationprocessing unit 30-1 to the suspend state in which the informationprocessing unit 30-1 is temporarily powered down (S620).

On the other hand, if a response is received which indicates that thedistribution data has not been received (S635: YES), then thedestination selection section 420 selects a destination informationprocessing unit to which the distribution data is to be sent (S640). Ifthe response which indicates that the distribution data has not beenreceived is received from a plurality of information processing units,then the destination selection section 420 preferably selects aninformation processing unit which communicates with the informationprocessing unit 30-1 at the highest speed from among those informationprocessing units.

For example, the destination selection section 420 may select aninformation processing unit having the highest wireless-LAN link speed.Alternatively, the destination selection section 420 may measure theeffective speed between the information processing unit 30-1 and each ofthe other information processing units, and select an informationprocessing unit having the highest effective speed. Alternatively, thedestination selection section 420 may select an information processingunit which communicates via a wireless LAN conforming to theIEEE802.11a/g standard without selecting any information processing unitwhich communicates via a wireless LAN conforming to the IEEE802.11bstandard. Accordingly, it is possible to assign a frequency band tohigher-speed communication and distribute the distribution dataefficiently.

The destination selection section 420 notifies the selected informationprocessing unit that the information processing unit has been selectedas the destination (S650). The destination selection section 420 alsonotifies each of the information processing units which have not beenselected as the destination among the information processing units whichhave made the response, that the information processing unit has notbeen selected as the destination (S655). Thereby, the notifiedinformation processing unit can shift its process to receipt of thedistribution data from another information processing unit. In thiscase, the destination selection section 420 preferably sends to each ofthe information processing units which have not been selected as thedestination among the information processing units which have made theresponse, information about the total number of the informationprocessing units which have made the response in association with thenotification that the information processing unit has not been selectedas the destination. Thereby, the information processing unit waiting toreceive the distribution data can know the approximate number ofinformation processing units which compete therewith to receive thedistribution data.

The distribution data sending section 430 then sends the distributiondata to the information processing unit selected by the destinationselection section 420, using the unused band detected by the unused banddetection section 410 (S660). When transmission of the distribution dataends, the waiting time setting section 425 sets a waiting time to waitbefore selecting a destination information processing unit to which thedistribution data is to be sent next, based on the time required forsending the distribution data (S665).

If the distribution data sending section 430 sends the distribution datato another information processing unit at a higher communication speed,then the waiting time setting section 425 preferably sets the waitingtime shorter in comparison with the case where the communication speedis lower. Thereby, it is possible to assign a frequency band to aninformation processing unit having a higher communication speedpreferentially and, therefore, distribute the distribution data moreefficiently. As an another example, if the number of HOPs or the numberof times the distribution data received by the distribution datareceiving section 400 has been transferred sequentially by a pluralityof information processing unit, is larger, then the waiting time settingsection 425 sets the waiting time shorter in comparison with the casewhere the number of HOPs is smaller. Thereby, it is possible todistribute the distribution data to an information processing unitlocated farther from the source information processing unitpreferentially to enhance efficiency of distributing the distributiondata.

Then, the power down section 450 determines whether or not the strengthor remaining charge of the battery 1068 is equal to or greater than theamount required for sending the distribution data (S670). For example,the power down section 450 may assume the battery strength capable ofdriving the information processing unit 30-1 for the time required forsending distribution data in the past to be the necessary amount.Alternatively, the power down section 450 may assume the batterystrength capable of driving the information processing unit 30-1 for thetime required for the distribution data receiving section 400 to receivethe distribution data to be the necessary amount and determine whetheror not the strength of the battery 1068 is equal to or greater than thenecessary amount. Thereby, it is possible to predict the necessaryamount at a certain level of accuracy even if the information processingunit has not sent the distribution data to another informationprocessing unit.

If the battery strength is equal to or greater than the necessary amount(S670: YES), then the destination selection section 420 waits for thewaiting time set by the waiting time setting section 425 (S680) andreturns the process to step S600. On the other hand, if the strength ofthe battery 1068 is below the necessary amount (S670: NO), then thepower down section 450 shuts down the information processing unit 30-1(S690), and the information processing unit 30-1 finishes the process.Thus, it is possible to prevent the battery from being exhausted duringtransmission of distribution data.

Alternatively, the power down section 450 may power down or shut downthe information processing unit 30-1 when the strength of the battery1068 is below a predetermined reference amount for the transmission ofdistribution data. For example, the power down section 450 powers downthe information processing unit 30-1 when the strength of the battery1068 is below 80% of the full charge. As a result, it is possible tokeep the battery strength of all the information processing units in theinformation processing system 10 at about 80% when distribution ofdistribution data ends. Thereby, it is possible to keep appropriatebattery strength when the information processing system 10 is used againafter the distribution data has been distributed.

FIG. 7 shows a process flow of the information processing unit 30-1receiving distribution data. The distribution data receiving section 400detects an inquiry about whether distribution data has not been received(S700). If such an inquiry is not detected (S710: NO), then thesuspending section 440 may temporarily power down the informationprocessing unit 30-1 to shift it to the suspend state (S720).

On the other hand, if such an inquiry is detected (S710: YES), then thedistribution data receiving section 400 responds that it has notreceived distribution data (S730). The distribution data receivingsection 400 then shifts to a reserved state in which it does not respondto an inquiry from any information processing unit other than theinquiring information processing unit that it has not receiveddistribution data (S740).

Then, if the distribution data receiving section 400 is notified thatthe information processing unit 30-1 has not been selected as adestination (S750: YES), the distribution data receiving section 400releases the reserved state (S760). The distribution data receivingsection 400 may receive information about the total number ofinformation processing units which have responded to the inquiry thatdistribution data has not been received, in association with thenotification that the information processing unit 30-1 has not beenselected as a destination. In this case, the suspending section 440preferably powers down the information processing unit 30-1 temporarilyfor a longer time when the total number of responding informationprocessing units is larger, in comparison with the case where the totalnumber of responding information processing units is smaller (S720).Thereby, it is possible to reduce power consumption wasted by waiting toreceive distribution data when there are a lot of information processingunits competing to receive the distribution data.

On the other hand, if the distribution data receiving section 400 is notnotified that the information processing unit 30-1 has not been selectedas a destination (S750: NO), then it determines whether or not it isnotified that the information processing unit 30-1 has been selected asa destination (S770). If the distribution data receiving section 400 isnot notified that the information processing unit 30-1 has been selectedas a destination (S770: NO), then it returns the process to step S750.If the distribution data receiving section 400 is notified that theinformation processing unit 30-1 has been selected as a destination(S770: YES), then it starts to receive the distribution data (S780).

The process of sending distribution data to each information processingunit as time passes will be described with reference to FIGS. 8 to 13.In FIGS. 8 to 13, the distribution data is assumed to be sent andreceived via a wireless LAN conforming to the IEEE802.11a/g standard.Therefore, bands available for one communication are twenty-sevenpredetermined channels among channels 1 to 165. In the figures, thesechannels are indicated at the horizontal axis. The vertical axis of thefigures indicates a lapse of time, and one space between horizontalsolid lines indicates a lapse of one hour. It is assumed here thattransmission of distribution data requires thirty minutes.

FIG. 8 shows a process of sending distribution data via wirelesscommunication in thirty minutes from the beginning. A source informationprocessing unit sends distribution data to another informationprocessing unit using the channel 1. FIG. 9 shows a process of sendingthe distribution data via wireless communication in one hour from thebeginning. Each of the source information processing unit and theinformation processing unit which has received the distribution datafrom the source information processing unit sends the distribution datato another information processing unit using the channel 1 and thechannel 6 in the next thirty minutes, respectively.

FIG. 10 shows a process of sending the distribution data via wirelesscommunication in one hour and thirty minutes from the beginning. Theinformation processing units which have received the distribution datain one hour from the beginning and the source information processingunit send the distribution data to other information processing unitsusing the channels 1, 6, 11 and 36, respectively. FIG. 11 shows aprocess of sending the distribution data via wireless communication intwo hours from the beginning. The information processing units whichhave received the distribution data in one hour and thirty minutes fromthe beginning and the source information processing unit send thedistribution data to other information processing units using thechannels 1, 6, 11, 36, 40, 44 and 48, respectively.

FIG. 12 shows a process of sending the distribution data via wirelesscommunication in two hours and thirty minutes from the beginning. Theinformation processing units which have received the distribution datain two hours from the beginning and the source information processingunit send the distribution data to other information processing unitsthrough the channel 1, 6, 11, 36, 40, 44, 48, 52, 56, 60, 64, 100, 104,108 and 112, respectively.

FIG. 13 shows a process of sending the distribution data via wirelesscommunication in three hours from the beginning. The informationprocessing units which have received the distribution data in two hoursand thirty minutes from the beginning and the source informationprocessing unit send the distribution data to other informationprocessing units through the channel 1, 6, 11, 36, 40, 44, 48, 52, 56,60, 64, 100, 104, 108, 112, 116, 120, 124, 128, 149, 153, 157, 161 and165, respectively. As a result, the distribution data is stored infifty-three information processing units in three hours.

As described above, with the information processing system 10 accordingto this embodiment, it is possible to efficiently distribute data usinga plurality of frequency bands at the same time even if each informationprocessing unit can use only one frequency band. Thereby, in comparisonwith the case of using an expensive communication device using aplurality of frequency bands at the same time, the same level ofcommunication speed can be achieved at a lower cost. Furthermore, evenif it is legally prohibited for one device to a plurality of frequencybands at the same time, high-speed communication can be realized byefficiently utilizing a plurality of frequency bands.

Furthermore, according to the embodiment, it is possible to save batteryconsumption in consideration of use after distribution of distributiondata. Thereby, it is possible to reduce burden on an administrator andgeneral users and enhance convenience for them in various applicationfields such as school education, various lectures and company training.

While the present invention has been described with reference topresently preferred embodiments, the technical scope of the presentinvention is not limited to the embodiment described above. It isapparent to those skilled in the art that various modifications orimprovements can be made to the embodiment described above. It isapparent from the appended claims that such modified or improvedembodiments can also be included in the technical scope of the presentinvention.

1. A method comprising: receiving distribution data at a firstinformation processing unit of an information processing system, wherethe distribution data is to be distributed to each of the informationprocessing units in the information processing system; selecting by thefirst information processing unit a destination information processingunit from among the information processing units of the informationprocessing system; and sending said distribution data from the firstinformation processing unit to the destination information processingunit using a first wireless frequency band that is not being used byother information processing units of the information processing systemto transmit the distribution data, where sending occurs at least in partwhile a second wireless frequency band is used by at least one of theother information processing units to transmit the distribution data. 2.The method according to claim 1, where the destination informationprocessing unit is the information processing unit of the informationprocessing system that communicates with the first informationprocessing unit at a highest speed.
 3. The method according to claim 1,further comprising: detecting an unused frequency band that is not usedby any information processing unit of the information processing systemthat is located within a range in which a radio wave of wirelesscommunication performed by that information processing unit interferes,where the first wireless frequency band is the detected unused frequencyband.
 4. The method according to claim 3, further comprising temporarilypowering down the first information processing unit and placing thefirst information processing unit in a suspended state if no unusedfrequency bands are detected.
 5. The method according to claim 1,further comprising: inquiring of other information processing units ofthe information processing system whether the distribution data has beenreceived, where selecting selects an information processing unit fromamong information processing units that respond that the distributiondata has not been received, notifying the destination informationprocessing unit that the destination information processing unit hasbeen selected as the destination information processing unit, andnotifying responding information processing units that have not beenselected as the destination information processing unit that thenon-selected information processing unit has not been selected as thedestination information processing unit.
 6. The method according toclaim 5, further comprising: in response to receiving at an inquiredinformation processing unit an inquiry whether an inquired informationprocessing unit has received the distribution data, determining whetherthe distribution data has already been received at the inquiredinformation processing unit; in response to determining that thedistribution data has not been received, responding that thedistribution data has not been received and placing the inquiredinformation processing unit in a reserved state, where while in thereserved state additional responses indicating that the distributiondata has not been received are not made in response to receivinginquiries by other information processing units; in response toreceiving a notification indicating that the information processing unithas been selected as the destination information processing unit,receiving the distribution data; and in response to receiving anotification indicating that the information processing unit has notbeen selected as the destination information processing unit, releasingthe reserved state.
 7. The method according to claim 5, furthercomprising: sending, to each of the responding information processingunits that have not been selected as the destination informationprocessing unit, information descriptive of a total number of theresponding information processing units; and temporarily powering downeach of the responding information processing units for a period of timethat is related to the total number of the responding informationprocessing units.
 8. The method according to claim 1, further comprisingtemporarily powering down the first information processing unit andswitching that information processing unit to a suspend state if thefirst information processing unit is not able to detect an informationprocessing unit that has not received the distribution data.
 9. Themethod according to claim 1, further comprising powering down the firstinformation processing unit without sending the distribution data inresponse to determining that the strength of a power source of the firstreceiving information processing unit is below an amount required forsending the distribution data.
 10. The method according to claim 9,further comprising powering down the selected destination informationprocessing unit in response to determining that the strength of a powersource of the selected destination information processing unit is belowan amount required for receiving the distribution data.
 11. The methodaccording to claim 1, further comprising in response to sending thedistribution data at a first communication speed, selecting a nextdestination information processing unit after a waiting time that is afunction of a communication speed of the next destination informationprocessing unit.
 12. The method according to claim 11, where the waitingtime is further a function of a number of HOPs which indicate a numberof times the distribution data has been transferred sequentially byinformation processing units.
 13. The method according to claim 1,further comprising acquiring a transfer route along which thedistribution data is transferred sequentially by information processingunits, where selecting the destination information processing unit isbased on the transfer route.
 14. The method according to claim 13,further comprising: acquiring used band indicating informationspecifying a frequency band to be used by each information processingunit for wireless communication; and detecting, based on the used bandindicating information, an unused band that is a frequency band not usedby any information processing unit located within a range in which aradio wave of wireless communication performed by that informationprocessing unit interferes.